Top emission type organic electroluminescent display device including X-ray shield layer and method of fabricating the same

ABSTRACT

A top emission type organic electroluminescent display device includes a first substrate including a pixel region, a switching thin film transistor and a driving thin film transistor in the pixel region on the first substrate, a passivation layer covering the switching thin film transistor and the driving thin film transistor and exposing a drain electrode of the driving thin film transistor, a connection electrode on the passivation layer and contacting the drain electrode of the driving thin film transistor, a partition wall corresponding to a border between adjacent pixel regions and overlapping an edge portion of the connection electrode, an x-ray shield layer on the connection electrode between adjacent partition walls, the x-ray shield layer automatically patterned in the pixel region due to the partition wall, a first electrode on the x-ray shield layer, a bank covering the partition wall and contacting an edge portion of the first electrode, an organic emission layer on the first electrode between adjacent banks, a second electrode on the organic emission layer, and a second substrate facing the first substrate and being transparent.

The present invention claims the benefit of Korean Patent ApplicationNo. 10-2008-0121273, filed in Korea on Dec. 2, 2008, which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent displaydevice, and more particularly, to a top emission type organicelectroluminescent display device and a method of fabricating the same.

2. Discussion of the Related Art

Among flat panel displays, organic electroluminescent displays, haveproperties of high brightness and low driving voltages. In addition,because they are self-luminous, the organic electroluminescent displayshave excellent contrast ratios and have ultra thin thicknesses. Theorganic electroluminescent displays have response time of several microseconds, and there are advantages in displaying moving images. Theorganic electroluminescent displays have wide viewing angles and arestable under low temperatures. Since the organic electroluminescentdisplays are driven by low voltage of direct current (DC) 5V to 15V, itis easy to design and manufacture driving circuits.

The organic electroluminescent displays are classified into a passivematrix type and an active matrix type. In the passive matrix type, scanlines and signal lines cross each other to form diodes, and the signallines are sequentially scanned to drive each pixel. To obtain requiredaverage brightness, instant brightness is needed which is the product ofaverage brightness and the number of lines.

On the other hand, in the active matrix type, a thin film transistor, asa switching element, is formed in each sub-pixel. A first electrodeconnected to the thin film transistor turns on/off by the sub-pixel, anda second electrode facing the first electrode functions as a commonelectrode. In addition, a voltage applied to the sub-pixel is stored ina storage capacitor, and the voltage is maintained until the signal ofnext frame is applied. Accordingly, regardless of the number of the scanlines, the sub-pixels are continuously driven during one frame. Eventhough low currents are applied, brightness may be constant. Therefore,recently, the active matrix type organic electroluminescent displayshave widely used because of their low power consumption, high definitionand large-sized possibility.

FIG. 1 is an equivalent circuit diagram illustrating a pixel of anactive matrix organic electroluminescent display device according to therelated art.

In FIG. 1, the pixel of the active matrix organic electroluminescentdisplay device includes a switching thin film transistor STr, a drivingthin film transistor DTr, a storage capacitor StgC, and an organicelectroluminescent diode E.

More particularly, a gate line GL is formed along a first direction. Adata line DL is formed along a second direction crossing the firstdirection and defines a pixel region P with the gate line GL. A powerline PL for supplying a source voltage is spaced apart from the dataline DL.

The switching thin film transistor STr is formed at a crossing portionof the gate line GL and the data line DL. The driving thin filmtransistor DTr is electrically connected to the switching thin filmtransistor STr. The organic electroluminescent diode E includes a firstelectrode connected to a drain electrode of the driving thin filmtransistor DTr and a second electrode connected to the power line PL.The power line PL supplies the source voltage to the organicelectroluminescent diode E. The storage capacitor StgC is formed betweena gate electrode and a source electrode of the driving thin filmtransistor DTr.

A scan signal is applied to the switching thin film transistor STrthrough the gate line GL, and the switching thin film transistor STrturns on. Then, a data signal from the data line DL is supplied to thegate electrode of the driving thin film transistor DTr, and the drivingthin film transistor DTr turns on. Accordingly, the organicelectroluminescent emits light. Here, when the driving thin filmtransistor DTr is in on-state, levels of currents flowing in the organicelectroluminescent diode E from the power line PL are determined. Theorganic electroluminescent diode E has gray scales according to thelevels of the currents. When the switching thin film transistor STrturns off, the storage capacitor StgC maintains a gate voltage of thedriving thin film transistor DTr constant. Even though the switchingthin film transistor STr is in off-state, the levels of the currentsflowing in the organic electroluminescent diode D are constantlymaintained until a next frame.

The organic electroluminescent display device is classified into a topemission type and a bottom emission type according to a direction oflight emitted from the organic electroluminescent diode. The bottomemission type has a disadvantage of low aperture ratio, and recently thetop emission type has been widely used.

FIG. 2 is a schematic cross-sectional view of a top emission typeorganic electroluminescent display device according to the related art.

In FIG. 2, first and second substrates 10 and 70 are disposed to faceeach other. Peripheries of the first and second substrates 10 and 70 aresealed by a seal pattern 80. A driving thin film transistor DTr isformed in each pixel region P on the first substrate 10. A passivationlayer 40 is formed on the driving thin film transistor DTr and has adrain contact hole 43. A first electrode 47 is formed on the passivationlayer 40 and contacts an electrode (not shown) of the driving thin filmtransistor DTr through the drain contact hole 43.

An organic emission layer 55 is formed on the first electrode 47 in eachpixel region P. The organic emission layer 55 includes red, green andblue organic luminous patterns 55 a, 55 b and 55 c each corresponding tothe pixel region P. A second electrode 58 is formed on the organicemission layer 55 all over the surface of the first substrate 10. Thefirst and second electrodes 47 and 58 provide electrons and holes. Thefirst electrode 47, the organic emission layer 55 and the secondelectrode 58 sequentially layered constitute an organicelectroluminescent diode E.

The first substrate 10 and the second substrate 70 are attached by theseal pattern 80, and the second electrode 58 on the first substrate 10is spaced apart from the second substrate 70.

FIG. 3 is a cross-sectional view of a pixel region of a top emissiontype organic electroluminescent display device according to the relatedart. The pixel region includes a driving thin film transistor.

In FIG. 3, the driving thin film transistor DTr is formed on a firstsubstrate 10. The driving thin film transistor DTr includes a gateelectrode 13, a gate insulating layer 16, a semiconductor layer 20including an active layer 20 a and ohmic contact layers 20 b, and sourceand drain electrodes 33 and 36 sequentially layered on the firstsubstrate 10. The active layer 20 a is formed of intrinsic amorphoussilicon. The ohmic contact layers 20 b are formed of impurity-dopedamorphous silicon and are spaced apart from each other on the activelayer 20 a. The source and drain electrodes 33 and 36 are spaced apartfrom each other and are connected to a power line (not shown) and anorganic electroluminescent diode E, respectively.

The organic electroluminescent diode E includes first and secondelectrodes facing each other and an organic emission layer 55 interposedtherebetween. The first electrode 47 is formed in each pixel region Pand contacts an electrode of the driving thin film transistor DTr. Thesecond electrode 58 is formed on the organic emission layer 55 all overthe surface of the first substrate 10.

A second substrate 70 for encapsulation is disposed over and faces thefirst substrate 10 including the above-mentioned elements, and the firstand second substrates 70 form an organic electroluminescent displaydevice 1.

In the top emission type organic electroluminescent display device 1,when the driving thin film transistor DTr is a p-type, the firstelectrode 47 is formed of a transparent conductive material havingrelatively high work function, such as indium tin oxide or indium zincoxide, so as to function as an anode electrode, and the second electrode58 is formed of a metallic material having relatively low work functionso as to function as a cathode electrode.

However, the metallic material, which is used for the second electrode58 functioning as the cathode electrode and has relatively low workfunction, is opaque. Therefore, if the opaque metallic material isdeposited to have a thickness of an ordinary electrode or insulatinglayer, that is, several thousand angstroms (Å), light cannot passthrough the second electrode 58, and the top emission cannot beachieved.

To keep its transparency, the second electrode 58, which is formed of anopaque metallic material having relatively low work function, may have adouble-layered structure including a lower layer (not shown) of anopaque metallic material and an upper layer (not shown) of a transparentconductive material, wherein the lower layer has a thickness of severalten angstroms (Å) to several hundred angstroms (Å), and the upper layerhas a thickness of several thousand angstroms (Å). With respect to thefirst electrode 47, which is formed of a transparent conductive materialhaving relatively high work function and functions as an anodeelectrode, a reflective layer (not shown) of a material havingrelatively high reflectivity is further formed under the first electrode47 to reflect light and increase emission efficiency.

However, the transparent conductive material is generally deposited by asputtering method. The sputtering method has a mechanism in which atomsor molecules are ejected from a target due to collision with particleshaving high energy and are adsorbed to a surface of a substrate.Accordingly, the atoms or particles have high energy and thus damage thesurface of the substrate or a treated material layer. Particularly,since an organic insulating layer is formed by a thermal depositionmethod and has a relatively weak surface, it is impossible to form atransparent conductive layer on the organic insulating layer by thesputtering method. In addition, when a transparent conductive layer isformed on a metallic layer, which is formed of a thermal depositionmethod, by the sputtering method, the metallic layer may be transformeddue to surface damage or may have poor functions because the particlesfrom the target penetrate into the metallic layer and lower theproperties of the metallic layer.

To solve the problem, an electron beam deposition method has beensuggested as a method for depositing a transparent conductive material.In the electron beam deposition method, an electron beam, which isgenerated from a thermal ion electron beam gun or a plasma electron beamgun, is irradiated to a target, and the target is partly heated andevaporated to thereby form a layer, which is made of a material for thetarget, on a surface of a substrate. Accordingly, there is no damage onthe surface of the substrate, and even though a film has a weak surface,a predetermined material layer can be formed on the film by the electronbeam deposition method without damage.

By the way, the electron beam method causes another problem. When theelectron beam is generated or the electro beam is irradiated to thetarget, X-ray is generated. The X-ray goes into the driving andswitching thin film transistors under the first electrode and decreasescharacteristics of the thin film transistors. Especially, when the X-rayis incident on a channel of a thin film transistor, off currents of thethin film transistor rapidly increase, and a threshold voltageincreases. Therefore, functions of the thin film transistor areremarkably lowered.

Accordingly, to form a film by the electron beam deposition method, ashield layer for blocking the X-ray is needed over the driving andswitching thin film transistors. The shield layer is formed of ametallic material having an atomic density of about 10 g/cm³ to about 30g/cm³, for example, tungsten or lead. Here, since lead has a relativelyvery low melting point, lead can be melted during a thermal depositionprocess, and tungsten may be used as an x-ray shield layer.

However, tungsten has been seldom used in the organic electroluminescentdisplay device, and it has not been considered that etchant for tungstenaffects elements of the organic electroluminescent display device.According to this, when etching tungsten, other elements may be removedtogether. Moreover, etching bath and rinse equipment for patterningtungsten are required, and this causes an increase in initial equipmentcosts.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a top emission typeorganic electroluminescent display device and a method of fabricatingthe same that substantially obviates one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a top emission typeorganic electroluminescent display device and a method of fabricatingthe same that include an x-ray shield layer for electron beamdeposition, wherein the x-ray shield layer is formed of tungsten andautomatically patterned by the pixel region.

Another object of the present invention is to provide a top emissiontype organic electroluminescent display device and a method offabricating the same that do not need additional equipment and costs.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a topemission type organic electroluminescent display device includes a firstsubstrate including a pixel region, a switching thin film transistor anda driving thin film transistor in the pixel region on the firstsubstrate, a passivation layer covering the switching thin filmtransistor and the driving thin film transistor and exposing a drainelectrode of the driving thin film transistor, a connection electrode onthe passivation layer and contacting the drain electrode of the drivingthin film transistor, a partition wall corresponding to a border betweenadjacent pixel regions and overlapping an edge portion of the connectionelectrode, an x-ray shield layer on the connection electrode betweenadjacent partition walls, the x-ray shield layer automatically patternedin the pixel region due to the partition wall, a first electrode on thex-ray shield layer, a bank covering the partition wall and contacting anedge portion of the first electrode, an organic emission layer on thefirst electrode between adjacent banks, a second electrode on theorganic emission layer, and a second substrate facing the firstsubstrate and being transparent.

In another aspect, a method of fabricating a top emission type organicelectroluminescent display device includes forming a switching thin filmtransistor and a driving thin film transistor in a pixel region on afirst substrate, forming a passivation layer over the switching thinfilm transistor and the driving thin film transistor, the passivationlayer having a drain contact hole exposing a drain electrode of thedriving thin film transistor, forming a connection electrode in thepixel region on the passivation layer, the connection electrodecontacting the drain electrode of the driving thin film transistorthrough the drain contact hole, forming a partition wall on theconnection electrode and corresponding to a border between adjacentpixel regions, the partition wall overlapping an edge portion of theconnection electrode having a width of a top surface wider than a widthof a bottom surface, forming an x-ray shield layer on the connectionelectrode and automatically separated in the pixel region due to thepartition wall by depositing tungsten over a substantially entiresurface of the first substrate, forming a first electrode on the x-rayshield layer and automatically separated in the pixel region due to thepartition wall, forming a bank of an inorganic insulating material, thebank covering the partition wall and contacting an edge portion of thefirst electrode, forming an organic emission layer on the firstelectrode between adjacent banks, forming a second electrode on theorganic emission layer by an electron beam deposition method, andattaching the first substrate and a second substrate such that a sealpattern is formed between the first and second substrates alongperipheries of the first and second substrates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is an equivalent circuit diagram illustrating a pixel of anactive matrix organic electroluminescent display device according to therelated art;

FIG. 2 is a schematic cross-sectional view of a top emission typeorganic electroluminescent display device according to the related art;

FIG. 3 is a cross-sectional view of a pixel region of a top emissiontype organic electroluminescent display device according to the relatedart. The pixel region includes a driving thin film transistor;

FIGS. 4A and 4B are cross-sectional views illustrating a top emissiontype organic electroluminescent display device according to a firstembodiment of the present invention;

FIGS. 5A to 5I are cross-sectional views of a substrate for a topemission type organic electroluminescent display device in steps ofmanufacturing the same according to the first embodiment of the presentinvention;

FIG. 6 is a graph showing current-voltage (I-V) curve characteristicsaccording to thicknesses of the x-ray shield layer, which is formed oftungsten;

FIGS. 7A and 7B are cross-sectional views illustrating a top emissiontype organic electroluminescent display device according to a secondembodiment of the present invention; and

FIGS. 8A to 8E are cross-sectional views of a substrate for a topemission type organic electroluminescent display device in steps ofmanufacturing the same according to the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, which are illustrated in the accompanyingdrawings.

FIGS. 4A and 4B are cross-sectional views illustrating a top emissiontype organic electroluminescent display device according to a firstembodiment of the present invention. FIG. 4A shows an example in which afirst electrode functions as an anode electrode, and FIG. 4B showsanother example in which the first electrode functions as a cathodeelectrode. For convenience of explanation, an area where a driving thinfilm transistor DTr is defined as a driving area TrA, and although notshown in the figures, an area where a switching thin film transistor isdefined as a switching area. In addition, FIGS. 4A and 4B have similarstructures except for first and second electrodes including differentlayers and materials, and the structure of FIG. 4A may be mainlydescribed.

As shown in the figures, the top emission type organicelectroluminescent display device 101 according to the present inventionincludes first and second substrates 110 and 170, wherein a driving thinfilm transistor DTr, a switching thin film transistor (not shown) and anorganic electroluminescent diode E are formed on the first substrate110, and the second substrate 170 is used for encapsulation.

More particularly, a gate line (not shown) and a gate electrode 113 areformed on the first substrate 110. The gate line is extended along afirst direction. The gate electrode 113 is disposed in each of thedriving area DA and the switching area (not shown). Although not shownin the figure, the gate electrode in the switching area is connected tothe gate line. A gate insulating layer 116 is formed on the gate line(not shown) and the gate electrode 113 all over the surface of the firstsubstrate 110. A data line (not shown) is formed on the gate insulatinglayer 116 and is extended along a second direction. The data linecrosses the gate line to define a pixel region P. A semiconductor layer120 is formed in each of the driving area TrA and the switching area(not shown) on the gate insulating layer 116 and corresponds to the gateelectrode 113. The semiconductor layer 120 includes an active layer 120a of intrinsic amorphous silicon and ohmic contact layers 120 b ofimpurity-doped amorphous silicon. The ohmic contact layers 120 b arespaced apart from each other on the active layer 120 a. Source and drainelectrodes 133 and 136 are formed and spaced apart from each other onthe ohmic contact layers 120 b. Although not shown in the figure, thesource electrode in the switching area is connected to the data line.

The gate electrode 113, the gate insulating layer 116, the semiconductorlayer 116, and the source and drain electrodes 133 and 136 sequentiallylayered in the driving area TrA form the driving thin film transistorDTr. Even though the driving thin film transistor DTr is a bottom gatetype, the structure shown in the figure is an example, and variousmodifications and changes can be made. For example, the driving thinfilm transistor DTr may have a top gate structure, which sequentiallyincludes a semiconductor layer of polycrystalline silicon, a gateinsulating layer, a gate electrode, an inter insulating layer withsemiconductor contact holes exposing the semiconductor layer, and sourceand drain electrodes spaced apart from each other and connected to thesemiconductor layer through the semiconductor contact holes. Theswitching thin film transistor (not shown) in the switching area (notshown) has the same structure as the driving thin film transistor DTr.

Next, a passivation layer 140 is formed over the driving thin filmtransistor DTr and the switching thin film transistor (not shown). Thepassivation layer 140 includes a drain contact hole 143 exposing thedrain electrode 136 of the driving thin film transistor DTr. Aconnection electrode 145 is formed on the passivation layer 140 in eachpixel region P. The connection electrode 145 is connected to the drainelectrode 136 of the driving thin film transistor DTr through the draincontact hole 143. The connection electrode 145 may be formed of atransparent conductive material, such as indium tin oxide or indium zincoxide, or may be formed of a metallic material having a relatively lowresistivity, for example, aluminum (Al), aluminum alloy such as aluminumneodymium (AlNd), copper (Cu), copper alloy or chromium (Cr).

A partition wall 148 is formed on the connection electrode 145 andcorresponds to a border between adjacent pixel regions P. The partitionwall 148 is undercut and has a cross-section of a mushroom-like shape,that is, an overhang shape in which an upper part has a wide width thana lower part. An x-ray shield layer 153 is formed on the connectionelectrode 145 and in the pixel region P surrounded by the partition wall148. The x-ray shield layer 153 is automatically separated and patterneddue to the partition wall 148. The x-ray shield layer 153 may be formedof a metallic material having an atomic density of about 10 g/cm³ toabout 30 g/cm³, for example, tungsten.

A first electrode 158 is formed on the x-ray shield layer 153. In FIG.4A, the first electrode 158 functions as an anode electrode and isformed of a conductive material having relatively high work function andbeing transparent, for example, indium tin oxide or indium zinc oxide.In FIG. 4B, the first electrode 158 functions as a cathode electrode andis formed of a metallic material having relatively low work function,for example, aluminum (Al) or aluminum alloy such as aluminum neodymium(AlNd). Here, in the same way as the x-ray shield layer 153, the firstelectrode 158 is automatically separated and patterned due to thepartition wall 148, which has the cross-section of the overhang shapeand surrounds the pixel region P, and is formed in each pixel region P.On the other hand, first and second dummy patterns 154 and 159, which,respectively, include the same materials as the x-ray shield layer 153and the first electrode 158, are sequentially formed on a top surfaceand a side surface of the partition wall 148.

A bank 160 of an inorganic insulating material is formed over thepartition wall 148. The bank 160 completely covers the first and seconddummy patterns 154 and 159. The bank 160 partially covers the firstelectrode 158, which is separated and formed by the pixel region P, thatis, the bank 160 overlaps edge portions of the first electrode 158.

An organic emission layer 162 is formed on the first electrode 147. Asecond electrode 165 is formed on the organic emission layer 162 and thebank 160 all over the surface of the first substrate 110. The first andsecond electrodes 158 and 165 and the organic emission layer 162interposed therebetween constitute the organic electroluminescent diodeE.

In FIG. 4A, the second electrode 165 should be formed of a metallicmaterial having relatively low work function, for example, aluminum (Al)or aluminum alloy such as aluminum neodymium (AlNd), so as to act as acathode electrode. By the way, if the metallic material is thicklydeposited, light does not pass through the metallic material.Accordingly, the second electrode 165 has a double-layered structureincluding a first layer 165 a of the metallic material and a secondlayer 165 b of a transparent conductive material, for example, indiumtin oxide or indium zinc oxide. The first layer 165 a is disposed underthe second layer 165 b and contacts the organic emission layer 162. Thefirst layer 165 a has a thickness such that transparency is maintained,that is, within a range of about 500 Å to about 3,000 Å. The secondlayer 165 b has a thickness of about 500 Å to about 3,000 Å. The secondlayer 165 b decreases resistance of the second electrode 165 to therebyprovide uniform voltages all over the surface of the first substrate110. If the second electrode 165 includes only the first layer 165 a,the second electrode 165 has too thin thickness, and an inner resistanceper unit area increases to cause an inner voltage drop. Therefore,voltages cannot be uniformly provided due to the inner voltage drop, andthis results in poor brightness. Thus, the second layer 165 b preventsthe problem.

Meanwhile, in FIG. 4B, the second electrode 165 serves as an anodeelectrode. The second electrode 165 has a single-layered structure andis formed of a transparent conductive material having a relatively highwork function, for example, indium tin oxide or indium tin oxide. Thesecond electrode 165 may have a thickness of about 500 Å to about 3,000Å. Since the second electrode 165 is formed of the transparentconductive material, it is not necessary that the second electrode 165have a relatively thin thickness, and the second electrode 165 can havea relatively enough thick thickness considering the inner resistance.

Although not shown in the figures, the organic emission layer 164 mayinclude a single layer or may include multiple layers of a holeinjection layer, a hole transporting layer, an emitting material layer,an electron transporting layer and an electron injection layer toimprove emission efficiency. In the case that the organic emission layer164 includes multiple layers, positions of the layers can be changedaccording to the functions of the first and second electrodes 158 and165. That is, in FIG. 4A where the first electrode 158 functions as theanode electrode and the second electrode 165 acts as the cathodeelectrode, the hole injection layer, the hole transporting layer, theemitting material layer, the electron transporting layer and theelectron injection layer are sequentially formed on the first electrode158. On the other hand, in FIG. 4B where the first electrode 158functions as the cathode electrode and the second electrode 165 acts asthe anode electrode, the electron injection layer, the electrontransporting layer, the emitting material layer, the hole transportinglayer and the hole injection layer are sequentially formed on the firstelectrode 158.

A transparent second substrate 170 faces and is spaced apart from thefirst substrate 110 having the above-mentioned elements. The secondsubstrates 170 is attached with the first substrate 110, whereinperipheries of the first and second substrates 110 and 170 are sealed bya seal pattern (not shown).

In the organic electroluminescent display device 101, the x-ray shieldlayer 153, which shields the switching thin film transistor (not shown)and the driving thin film transistor DTr, more particularly, shieldschannel areas, is formed of tungsten and is automatically separated andpatterned into each pixel region P by the partition wall 148 having areversely tapered cross-section. Accordingly, the elements over thex-ray shield layer 153 can be formed by an electron beam depositionmethod.

A method of manufacturing a top emission type organic electroluminescentdisplay device according to the first embodiment of the presentinvention will be described hereinafter in detail with reference toaccompanying drawings.

FIGS. 5A to 5I are cross-sectional views of a substrate for a topemission type organic electroluminescent display device in steps ofmanufacturing the same according to the first embodiment of the presentinvention. Here, for example, switching and driving thin filmtransistors have a bottom gate structure and include intrinsic amorphoussilicon as an active layer.

In FIG. 5A, a gate line (not shown) and a gate electrode 113 are formedon an insulating layer 110 by depositing a metallic material havingrelatively low resistivity and patterning it through a mask process. Themask process may include applying photoresist to the metallic material,exposing the photoresist to light, developing the light-exposedphotoresist and etching the metallic material. The gate line is extendedalong a first direction. The gate electrode 113 is disposed in a drivingarea TrA. Although not shown in the figure, a gate electrode is alsoformed in a switching area, where the switching thin film transistor isdisposed, and is connected to the gate line.

A gate insulating layer 116 is formed on the gate line and the gateelectrode 113 all over the surface of the substrate 110. A semiconductorlayer 120 is formed on the gate insulating layer 116 over the gateelectrode 113. The semiconductor layer 120 includes an active layer 120a of intrinsic amorphous silicon and ohmic contact layers 120 b ofimpurity-doped amorphous silicon. The ohmic contact layers 120 b arespaced apart from each other over the active layer 120 a. Source anddrain electrodes 133 and 136 are formed on the ohmic contact layers 120b and are spaced apart from each other. The gate electrode 113, the gateinsulating layer 116, the semiconductor layer 120, and the source anddrain electrodes 133 and 136 in the driving area TrA form the drivingthin film transistor DTr. The switching thin film transistor (not shown)having the same structures as the driving thin film transistor DTr isformed in the switching area (not shown). Here, the semiconductor layer120 and the source and drain electrodes may be formed through differentmask processes or may be formed through the same mask process.

In the meantime, although not shown in the figure, a data line is formedon the gate insulating layer 116 through the same process as the sourceand drain electrodes 133 and 136. The data line is extended along asecond direction and crosses the gate line to define a pixel region P. Asource electrode (not shown) of the switching thin film transistor isconnected to the data line.

In the first embodiment of the present invention, even though thedriving and switching thin film transistors have a bottom gatestructure, the driving and switching thin film transistors many have atop gate structure including polycrystalline silicon.

Next, a passivation layer 140 is formed on the driving thin filmtransistor DTr and the switching thin film transistor (not shown) byapplying an organic insulating material, for example, benzocyclobutene(BCB) or photo acryl. The passivation layer 140 has a flat surface. Thepassivation layer 140 is patterned through a mask process to therebyform a drain contact hole 143 exposing the drain electrode 136 of thedriving thin film transistor DTr.

In FIG. 5B, a connection electrode 145 is formed in each pixel region Pon the passivation layer 140 having the drain contact hole 143 bydepositing a conductive material by a sputtering method and thenpatterning it through a mask process. The conductive material may be oneof aluminum (Al), aluminum alloy such as aluminum neodymium (AlNd),copper (Cu), copper alloy, chromium (Cr), indium tin oxide and indiumzinc oxide. The connection electrode 145 is connected to the drainelectrode 136 of the driving thin film transistor DTr through the draincontact hole 140.

In FIG. 5C, sacrificial patterns 146 are formed on the connectionelectrode 145 by depositing a sacrificial layer (not shown) andpatterning it through a mask process. The sacrificial layer may beformed of a conductive material, which can be wet-etched and etchant ofwhich does not affect the material for the connection electrode 145, forexample, molybdenum (Mo). The sacrificial patterns 146 are respectivelydisposed at both sides of a border between adjacent pixel regions P andoverlap edge portions of the pixel region P. The sacrificial patterns146 may have a thickness of about 2,500 Å to about 5,500 Å, which,desirably, is thicker than a sum of thicknesses of an x-ray shield layerand a first electrode to be formed later. The sacrificial patterns 146have a double dam structure in a plan view, wherein the sacrificialpatterns 146 are spaced apart from each other along the edge portions ofthe pixel region P at the both sides of the border between adjacentpixel regions P.

In FIG. 5D, an organic insulating material layer (not shown) is formedon the sacrificial patterns 146 all over the surface of the substrate110 and is patterned through a mask process to thereby form a partitionwall 148. The organic insulating material layer may be formed byapplying an organic insulating material, for example, benzocyclobutene(BCB), photo acryl or polyimide, and the organic insulating materiallayer may be thicker than the sacrificial patterns 146 such that thesacrificial patterns 146 are completely covered. The partition wall 148includes a lower part 148 a and an upper part 148 b. The lower part 148a of the partition wall 148 corresponds to an area between thesacrificial patterns 146 having the double dam structure at the borderbetween adjacent pixel regions P. The upper part 148 b of the partitionwall 148 is disposed over the lower part 148 a and has a wider widththan the lower part 148 a. The partition wall 148 has a cross-section ofa mushroom-like shape. The partition wall 148 overlaps and fills thedrain contact hole 143.

In FIG. 5E, a wet-etching step is carried out to the substrate 110including the partition wall 148 to thereby remove the sacrificialpatterns 146 of FIG. 5D under the upper part 148 b of the partitionwall. Accordingly, the upper part 148 of the partition wall 148 has anoverhang shape as against the lower part 148 a, and the lower part 148 ahas an undercut shape as against the upper part 148 b.

In FIG. 5F, an x-ray shield layer 153 is formed on the connectionelectrode 145 over the substrate 110, wherein the sacrificial patterns146 of FIG. 5E are removed, and a first electrode 158 is formed on thex-ray shield layer 153. Furthermore, first and second dummy patterns 154and 159 are sequentially formed on a top surface and a side surface ofthe partition wall 148. The first and second dummy patterns 154 and 159,respectively, include the same materials as the x-ray shield layer 153and the first electrode 158.

More particularly, a metallic material having an atomic density of about10 g/cm³ to about 30 g/cm³ is deposited all over the surface of thesubstrate 110 including the partition wall 148, and the x-ray shieldlayer 153 is automatically separated by the pixel region P due to thepartition wall 148. The metallic material, for example, may be tungsten,which has an atomic density of about 19.25 g/cm³. The x-ray shield layer153 covers the driving thin film transistor DTr in the driving area TrAand the switching thin film transistor (not shown) in the switchingregion (not shown).

It is desirable that the x-ray shield layer 153 has a thickness within arange of about 2,000 Å to 2,500 Å. If the x-ray shield layer 153 has athickness less than 2,000 Å, the x-ray shield layer 153 does notcompletely shield X-ray incident on the driving thin film transistor DTrand the switching thin film transistor (not shown). In this case,off-current characteristics are better than a device without the x-rayshield layer, but they are higher than reference, so that thetransistors cannot be used as a switching or driving element.

FIG. 6 is a graph showing current-voltage (I-V) curve characteristicsaccording to thicknesses of the x-ray shield layer, which is formed oftungsten.

In FIG. 6, when the x-ray shield layer of tungsten has the thickness ofabout 500 Å to about 1,000 Å, off-currents are considerably high ascompared with the reference, which is shown as an I-V curve of a thinfilm transistor that is not exposed to X-ray. Additionally, the I-Vcurves are different from each other. On the other hand, when the x-rayshield layer has the thickness of about 2,000 Å, the I-V curve issimilar to the reference, and there is almost no change in off-currents.

Meanwhile, a transparent conductive material having relatively high workfunction is formed all over the surface of the substrate 110 includingthe x-ray shield layer 153 by an electron beam deposition method or asputtering method, and the first electrode 158 is separated by the pixelregion P due to the partition wall 148. The transparent conductivematerial may be indium tin oxide or indium zinc oxide. The firstelectrode 158, beneficially, has a thickness within a range of about 500Å to about 3,000 Å. Here, the first electrode 158 functions as an anodeelectrode, and the x-ray shield layer 153 under the first electrode 158acts as a reflector.

Referring to FIG. 4B, when the first electrode 158 functions as acathode electrode, the first electrode 158 may be formed of a metallicmaterial having relatively low work function and high reflectivity, forexample, aluminum (Al), aluminum alloy such as aluminum neodymium (AlNd)or silver (Ag), by an electron beam deposition method. At this time, asstated above, the first electrode 158 may be automatically separated bythe pixel region P due to the partition wall 148. It is desirable thatthe first electrode 158 has a thickness within a range of about 500 Å to3,000 Å. Within the range, the first electrode 158 is opaque, and thefirst electrode 158 functions as a reflector to maximize efficiency in atop emission mode.

Next, in FIG. 5G, an inorganic insulating layer (not shown) is formed ona substantially entire surface of the substrate 110 including the firstelectrode 158 by depositing an inorganic insulating material and then ispatterned through a mask process, thereby forming a bank 160 over thepartition wall 148. The inorganic insulating material may be siliconoxide (SiO₂) or silicon nitride (SiN_(x)), for example. The bank 160entirely covers the second dummy pattern 159, which is formedsimultaneously with the first electrode 158, and both ends of the bank160 contact edge portions of the first electrode 158.

The inorganic insulating layer is not separated by the pixel region Pdifferently from the first electrode 158 and the x-ray shield layer 153thereunder. The inorganic insulating layer is continuously formed overthe first electrode 158 and the partition wall 148 with a predeterminedthickness. Since a distance between a top surface of the pixel region Pand a bottom surface of the upper part 148 b, that is, a distancebetween the connection electrode 145 and the upper part 148 b, is largerthan a total thickness of the x-ray shield layer 153 and the firstelectrode 158, the x-ray shield layer 153 and the first electrode 158are disconnected by the pixel region P. However, after forming the x-rayshield layer 153 and the first electrode 158, a distance between a topsurface of the pixel region P and the bottom surface of the upper part148 b, that is, a distance between the first electrode 158 and the upperpart 148 b, decreases due to the x-ray shield layer 153 and the firstelectrode 158. Therefore, the inorganic insulating layer can becontinuously formed by depositing the inorganic insulating materialthicker than the distance between the first electrode 158 and the upperpart 148 b.

In FIG. 5H, an organic emission layer 162 is formed in the pixel regionP between adjacent banks 160. The organic emission layer 162 is disposedon the first electrode 158 and the bank 160. The organic emission layer162 may include red, green and blue organic luminous patterns eachcorresponding to the pixel region P and sequentially arranged. In thiscase, the organic emission layer 162 may be formed by a thermaldeposition method using a shadow mask (not shown). Alternatively, theorganic emission layer 162 may include a white luminous material allover the surface of the substrate 110. At this time, the organicemission layer 162 may be formed by a nozzle coating method or a spincoating method.

In FIG. 5I, a second electrode 165 is formed on the organic emissionlayer 162. The second electrode 165 functions as a cathode electrode andhave a double-layered structure. More particularly, the second electrode165 includes a first layer 165 a of a metallic material havingrelatively low work function and a second layer 165 b of a transparentconductive material on the first layer 165 a. The first layer 165 a maybe formed by depositing one of aluminum (Al), aluminum alloy of aluminumneodymium (AlNd) and silver (Ag) by an electron beam deposition method.The first layer 165 a may have a thickness of about 5 Å to about 50 Åsuch that light passes through the first layer 165 a. The second layer165 b may be formed by depositing indium tin oxide or indium zinc oxideby an electron beam deposition method. The second layer 165 b may have athickness of about 500 Å to about 2,000 Å. The first layer 165 a has avery thin thickness so as to keep transparency, and its inner resistancerelatively increases. Voltage drops partially occur, and this causesproblems in brightness. To solve the problems, the second layer 165 bhaving a common thickness of electrodes is further formed on the firstlayer 165 b and prevents an increase of the inner resistance due to thethin thickness.

Meanwhile, the second electrode may function as an anode electrode asillustrated in FIG. 4B. In this case, the second electrode 165 may beformed to have a thickness of about 500 Å to about 3,000 Å by depositinga transparent conductive material having relatively high work function,for example, indium tin oxide or indium zinc oxide, on the organicemission layer 162 by an electron beam deposition method.

Next, although shown in the figures, a transparent substrate (not shown)is disposed over the substrate 110 including the above-mentionedelements thereon, wherein a seal pattern (not shown) is formed on one ofthe substrates along its periphery, and the substrates are attached tocomplete the top emission type organic electroluminescent display device101 of FIGS. 4A and 4B according to the first embodiment of the presentinvention. A moisture absorption pattern (not shown) having ahygroscopic property may be further formed inside the seal pattern.

FIGS. 7A and 7B are cross-sectional views illustrating a top emissiontype organic electroluminescent display device according to a secondembodiment of the present invention. FIG. 7A shows an example in which afirst electrode functions as an anode electrode, and FIG. 7B showsanother example in which the first electrode functions as a cathodeelectrode. The device according to the second embodiment has the sameelements as the first embodiment except for the partition wall. In thesecond embodiment, explanation for the same parts as the firstembodiment will be omitted.

In FIGS. 7A and 7B, the partition wall 248 is formed on the connectionelectrode 245 and corresponds to a border between adjacent pixel regionsP. The partition wall 248 is formed of an inorganic insulating materialor an organic insulating material. The partition wall 248 has across-section of a reversely tapered shape, a width of which increasesfrom the bottom to the top with respect to the connection electrode 245.

Accordingly, the x-ray shield layer 253 and the first electrode 258 areseparated by the pixel region P due to the partition wall 248 having thereversely tapered cross-section and are sequentially disposed on theconnection electrode 245. Here, ends of the x-ray shield layer 253 maybe substantially coincident with ends of the first electrode 258 becauseof the reversely tapered structure of the partition wall 248. The firstand second dummy patterns 254 and 259, which, respectively, include thesame materials as the x-ray shield layer 253 and the first electrode258, are sequentially formed on the partition wall 248 having thereversely tapered shape.

In the first embodiment, since the partition wall has the mushroom-likeshape, the first and second dummy patterns are formed on the topesurface and the side surface of the partition wall. Therefore, the x-rayshield layer, which is formed in the pixel region before the firstelectrode, has a wider width than the first electrode, that is, thefirst electrode on the x-ray shield layer has a narrower width than thex-ray shield layer. Ends of the x-ray shield layer are not coincidentwith ends of the first electrode.

However, in the second embodiment, the first and second dummy patterns254 and 259 are not formed on the side surface of the partition wall248. Accordingly, the x-ray shield layer 253 and the first electrode 258have the same width, and the ends of the x-ray shield layer 253 arecoincident with the ends of the first electrode 258.

Here, it is beneficial that a height of the partition wall 248 from thetop surface of the connection electrode 245, that is, a distance betweenthe top surface of the partition wall 248 and the top surface of theconnection electrode 245, is larger than a total thickness of the x-rayshield layer 253 and the first electrode 258. More particularly, theheight of the partition wall 248 from the top surface of the connectionelectrode 248, desirably, is within a range of about 110% to about 120%of the total thickness of the x-ray shield layer 253 and the firstelectrode 258 so that the bank 260, which covers the partition wall 248and the first and second dummy patterns 254 and 259, is not disconnectedbetween the partition wall 248 and the first electrode 258. The bank 260has a thicker thickness than a distance between the top surface of thepartition wall 248 and the top surface of the first electrode 258.

Hereinafter, a method of manufacturing a top emission type organicelectroluminescent display device according to the second embodiment ofthe present invention will be described in detail with reference toaccompanying drawings. The method according to the second embodiment hasthe same steps as the first embodiment except for forming the partitionwall. Therefore, explanation for the same steps as the first embodimentwill be omitted.

FIGS. 8A to 8E are cross-sectional views of a substrate for a topemission type organic electroluminescent display device in steps ofmanufacturing the same according to the second embodiment of the presentinvention.

In FIG. 8A, an inorganic insulating layer 247 is formed substantiallyall over the surface of the substrate 210 by depositing an inorganicinsulating material, for example, silicon oxide (SiO₂) or siliconnitride (SiN_(x)) on the connection electrode 245, which contacts thedrain electrode 236 of the driving thin film transistor DTr through thedrain contact hole 243 and is formed on the passivation layer 240, usingchemical vapor deposition apparatus. Since the connection electrode 245has a substantially even surface without steps, the inorganic insulatinglayer 247 also has a substantially flat surface all over the surfaceexcept for a portion corresponding to the drain contact hole 243. Eventhough the portion corresponding to drain contact hole 243 is shown flatin the figure, a recession may be formed due to the depositionproperties of the inorganic insulating material. However, this is not aproblem because the drain contact hole 243 has a relatively very smallsize as compared to the pixel region P.

A thickness of the inorganic insulating layer 247 is thicker than a sumof thicknesses of the x-ray shield layer and the first electrode to beformed later. Beneficially, the inorganic insulating layer 247 may havea thickness of about 3,000 Å to 5,000 Å. At this time, a deposition rateof the inorganic insulating material is relatively high at first, andthe deposition rate is gradually decreased such that the inorganicinsulating layer 247 has a relatively low density near by the connectionelectrode 253 and has an increasing density according as it becomes farfrom the connection electrode 253.

Next, a photoresist layer 291 is formed all over the surface by applyingphotoresist on the inorganic insulating layer 247, and the photoresistlayer 291 is exposed to light through a mask 195 including alight-transmitting portion TA and a light-blocking portion BA.

In FIG. 8B, the light-exposed photoresist layer 291 of FIG. 8A isdeveloped to thereby form a photoresist pattern 292 on the inorganicinsulating layer 247. The photoresist pattern corresponds to the borderbetween adjacent pixel regions P.

Isotropic dry-etching is applied to the inorganic insulating layer 247exposed by the photoresist pattern 292. In the isotropic dry-etching, athickness of the inorganic insulating layer 247 decreases at its upperand side surfaces. The etch rate at the upper surface of the inorganicinsulating layer 247 is higher than the etch rate at the side surface ofthe inorganic insulating layer 247. The etch rate at the side surface ofthe inorganic insulating layer 247 decreases as it approaches thephotoresist pattern 292. Moreover, since the inorganic insulating layer247 has a decreasing density from the top surface to the bottom surface,the etch rate near by the bottom surface, which is close to theconnection electrode 245, is higher than the etch rate near by the topsurface. Accordingly, in an area around the connection electrode 245,the side surface of the inorganic insulating layer 247 is faster etchednear by the bottom surface than near by the upper surface, and as shownin FIG. 8C, the partition wall 247 having a reversely taperedcross-section is formed.

In FIG. 8D, the photoresist pattern 292 of FIG. 8C on the partition wall248 is removed by performing a stripping or ashing step.

In FIG. 8E, the same steps as the first embodiment are applied to thepartition wall 248 having the reversely tapered structure and theconnection electrode exposed by the partition wall 248, whereby thex-ray shield layer 253 and the first electrode 258 are automaticallyseparated by the pixel region P due to the partition wall 248, and theorganic emission layer 262 and the second electrode 265 are sequentiallyformed. Therefore, completed is the substrate for the organicelectroluminescent display device according to the second embodiment ofthe present invention.

Next, referring to FIG. 7A, the transparent substrate 270 is disposedover the substrate 210 including the above-mentioned elements thereon,wherein a seal pattern (not shown) is formed on one of the substrates210 and 270 along its periphery, and the substrates 210 and 270 areattached to complete the top emission type organic electroluminescentdisplay device 201 according to the second embodiment of the presentinvention. A moisture absorption pattern (not shown) having ahygroscopic property may be further formed inside the seal pattern.

As another example of the second embodiment, the partition wall may beformed on an organic insulating material. More particularly, an organicinsulating material layer (not shown) having a flat surface may beformed on the connection electrode by applying a photosensitive organicinsulating material. The organic insulating material layer may beexposed to light and developed to thereby form the partition wall havingthe reversely tapered cross-section. At this time, the organicinsulating material may have a negative photosensitive property, inwhich a portion exposed to light remains after developing. In a negativephotosensitive material, a portion exposed to light is not removedbecause chemical reactions with light strongly occurs according tointensity of light and exposing time. When the organic insulatingmaterial layer is exposed to light, there is a difference in theintensities of light reaching the top surface and the bottom surface ofthe organic insulating material layer. That is, the intensity of lightis relatively high at the top surface of the organic insulating materiallayer, and the photosensitive organic insulating material sufficientlyreacts with light, whereby the portion exposed to light substantiallyentirely remains after developing. However, the intensity of lightdecrease toward the bottom surface of the organic insulating materiallayer, and specially, light is diffused around a border between thelight-transiting portion and the light-blocking portion due torefraction, etc. Therefore, the photosensitive organic material does notsufficiently react with light. According to this, the partition wall ofthe organic insulating material has the reversely tapered cross-sectionafter light-exposing and developing.

In the top emission type organic electroluminescent display device,since the x-ray shield layer of tungsten is formed over the switching ordriving thin film transistor, X-ray incident on the channel of the thinfilm transistor can be blocked. Thus, an electron beam deposition methodcan be used, and the properties of the thin film transistor can beprevented from being lowered due to the electron beam deposition method.

In addition, the x-ray shield layer of tungsten is automaticallypatterned by the pixel region, and a wet-etching process for patteringcan be omitted. Therefore, costs for additional equipment are notrequired.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A top emission organic electroluminescent display device, comprising: a first substrate including a pixel region; a switching thin film transistor and a driving thin film transistor in the pixel region on the first substrate; a passivation layer covering the switching thin film transistor and the driving thin film transistor and exposing a drain electrode of the driving thin film transistor; a connection electrode on the passivation layer and contacting the drain electrode of the driving thin film transistor; a partition wall corresponding to a border between adjacent pixel regions and overlapping an edge portion of the connection electrode; an x-ray shield layer on the connection electrode between adjacent partition walls, the x-ray shield layer patterned in the pixel region due to the partition wall such that the x-ray shield layer is formed between the adjacent partition walls; a first electrode on the x-ray shield layer; a bank covering the partition wall and contacting an edge portion of the first electrode; an organic emission layer on the first electrode between adjacent banks; a second electrode on the organic emission layer; and a second substrate facing the first substrate and being transparent.
 2. The display device according to claim 1, wherein the x-ray shield layer includes tungsten and has a thickness of about 2,000 Å to about 2,500 Å.
 3. The display device according to claim 1, wherein the partition wall has a cross-section of a reversely tapered shape with respect to connection electrode.
 4. The display device according to claim 3, wherein a height of the partition wall from a top surface of the connection electrode is larger than a sum of thicknesses of the x-ray shield layer and the first electrode.
 5. The display device according to claim 1, wherein the partition wall has a cross-section of a mushroom-like shape including a first part and a second part, which is disposed on the first part and has a wider width than the first part.
 6. The display device according to claim 5, wherein a distance between the connection electrode and the second part of the partition wall is larger than a sum of thicknesses of the x-ray shield layer and the first electrode.
 7. The display device according to claim 1, wherein the first electrode includes a transparent conductive material, and the second electrode includes a first layer and a second layer on the first layer, wherein the first layer has lower work function than the first electrode and has a thickness of about 5 Å to 50 Å, and the second layer includes a transparent conductive material and has a thickness of about 500 Å to 3,000 Å.
 8. The display device according to claim 7, wherein the first layer includes one of aluminum, aluminum alloy and silver.
 9. The display device according to claim 1, wherein the second electrode has higher work function than first electrode, wherein the first electrode includes one of aluminum, aluminum alloy and silver, and the second electrode includes a transparent conductive material.
 10. The display device according to claim 1, further comprising first and second dummy patterns sequentially disposed on the partition wall, wherein the first and second dummy patterns are formed of the x-ray shield layer and the first electrode, respectively. 